1. Field of the Invention
The present invention relates to a diagnostic system using a nuclear magnetic resonance phenomenon wherein a nuclear magnetic resonance signal receiving coil is inserted into a human body and a nuclear magnetic resonance image is formed.
2. Description of the Related Art
Conventionally, in the detection and diagnosis of a surface of a digestive organ of a human body, particularly to epidermal cancer generated in stomach walls or an upper layer of the intestinal canal, the general method was that the generated portion was detected by an endoscope or an X-ray diagnosis, and tissues of a living body of the generated portion was picked up, and was determined whether it is malignant or not.
However, in such a conventional method, since the sampling portion became a relatively wide range, there were problems in that the result of the diagnosis was not able to be determined, and it took much time to pick up the tissues of the living body, and the human body was damaged.
On the other hand, there has recently been widely used a non-attacking diagnosing method for a human body which utilizes a nuclear-magnetic resonance phenomenon (the nuclear-magnetic resonance being hereinafter referred to as the "MR"). With a magnetic resonance imaging device (the magnetic resonance imaging being hereinafter referred to as the "MRI"), a human body is placed in a static magnetic field, and a predetermined high frequency magnetic field is applied to the human body to excite nuclei having spins of the tissues in the body cavity of the human body. MR signals having a predetermined frequency produced until the excited nuclei return to the original positions are detected and processed by a computer to obtain vertical cross-sectional images of the body cavity of the human body.
The cross-sectional image obtained by the MRI device is extremely effective for diagnosis such as distinction between abnormal cells (such as cancer cells) and normal cells. It is known that MR signals from cancer tissues and normal tissues are generated at different relaxation time. Therefore, it is possible to diagnose whether the living tissues to be examined are cancer cells or not by imaging a difference between the MR signals in density based on the relaxation time.
Fine and accurate images must be obtained to diagnose diseases of the digestive system such as a tubular viscus and particularly to find the depths of its affected portions. However, since the MR signal receiving body coil is provided externally of a patient's body with the conventional apparatus, it is difficult to obtain fine and accurate cross sectional images of depth portions of the tubular viscus of the patient. For example, with a conventional system, a surface coil for receiving MR signals is placed on the abdomen of a patient and receives MR signals to diagnose the stomach walls. However, the signal-to-noise ratio (hereinafter referred to as the "SN ratio") is too low to obtain images sufficient for required diagnosis.
In order to overcome this problem, there has been proposed an insertion apparatus such as an endoscope or a probe, which is provided, on the distal end of an insertion section inserted in the body of a patient, with an MR signal receiving high frequency coil, for detecting MR signals, as disclosed in Published Examined Japanese Patent Application No. 3-5174 and Published Unexamined Patent Application No. 2-277440. With them, a coil inserted in the patient's body receives MR signals and provides fine and accurate images having a good SN ratio. Thus, fine and accurate images can be obtained for diagnosing the depths of affected portions of tubular viscus.
However, the conventional nuclear magnetic resonance diagnostic apparatus is structured as shown in FIG. 1. More specifically, reference numeral 1 is an MRI apparatus, which comprises an MR signal measuring device 2. On the other hand, in the inside of a top end portion of an insertion section 5 of an endoscope 4 inserted to the body cavity of a patient 3, a high frequency coil, which is an MR antenna for receiving an MR signal.
The high frequency coil is connected to a cable 8 through a matching circuit arranged in the top end portion 5 of the endoscope 4. The matching circuit matches impedance between the high frequency coil and the cable 8, and the cable 8 transmits the MR signal received by the high frequency coil. The cable 8 is connected to the MR signal measuring device 2 through a front amplifier 9, and a universal cord 10 of the endoscope is connected to a light power source device 11.
In such a conventional nuclear magnetic resonance diagnostic apparatus, the high frequency coil provided in the insertion section 5 of the endoscope 4 is not electrically insulated/separated from the nuclear magnetic resonance signal measuring device 2. In other words, in the endoscope with the built-in high frequency coil or the probe, the portion including the matching circuit and the cable 8 is in an electrically conductive live state.
In the conventional endoscope 4 or the probe, if the outer sheath of the insertion portion 5 is broken and the high frequency coil 6 and the mucous membrane of the living body is in a conductive state, there is fear that leakage current a will flow to the patient 3.